Hly176B, a low-salt tolerant halolysin from the haloarchaeon Haloarchaeobius sp. FL176

Extracellular proteases of haloarchaea are adapted to function at high concentrations of NaCl, and could find useful applications in industrial or biotechnological processes where hypersaline conditions are desired. The diversity of extracellular proteases produced by haloarchaea is largely unknown, although the genomes of many species have been sequenced and are publicly available. In this study, a gene encoding the extracellular protease Hly176B from the haloarchaeon Haloarchaeobius sp. FL176 was cloned and expressed in Escherichia coli. The catalytic triad Asp-His-Ser was confirmed via site-directed mutagenesis, indicating that Hly176B belongs to the class of serine proteases (halolysin). Unlike previously reported extracellular proteases from haloarchaea, Hly176B remained active in almost salt-free solution for a relatively long time. In addition, Hly176B displayed good tolerance to some metal ions, surfactants and organic solvents, and exerts its highest enzyme activities at 40 °C, pH 8.0 and 0.5 M NaCl. Therefore, this study enriches our knowledge of extracellular proteases, and also expands their applications in various industrial uses.